1. Field of the Invention
The present invention relates to a simple communication system capable of message broadcasting, and more particularly, to a terminal control system in an integrated services digital network (ISDN) exchange system, for example.
2. Description of the Related Art
In a prior art ISDN exchange system, a plurality of terminals are connected to a call control unit which is also connected to a plurality of supplementary service units such as a transfer service unit and a call-waiting service unit. In this ISDN exchange system, there is provided a memory unit having a group supervisory table for storing a relationship between group numbers and the terminals belonging thereto for message broadcasting. When a destination call message supplied to the call control unit includes supplementary services, the corresponding supplementary service unit carries out a message broadcasting operation in accordance with the group supervisory table. This will be explained later in detail.
In the above-mentioned prior art ISDN exchange system, however, since each of the supplementary service units needs to incorporate a grouping function for message broadcasting using the group supervisory table, the entire ISDN exchange system becomes complex.